IN NATURAL CLASSIFICATION. 587 
Boraginee, has a simple pollen—an exception to the general 
rule. 
The mode of dehiscence of the pollen is a character that 
has as yet been little studied.  Fritzche, Méhl and myself 
have contributed somewhat towards the history of this func- 
tion; and we have at least established, that it is a subject 
worthy of the most extensive examination. It is by means 
of re-agents, that the specific manner of dehiscence can alone 
be ascertained. The pollen bursting on the stigma, is acted 
upon by such variable forces, as to M i a general rule im- 
possible to be arrived at: and I have elsewhere shown, that 
the cause of rupture in such case is exactly identical with 
that which operates when the pollen, in the field of the 
microscope, is acted upon by dilute acids: it is, in truth, 
the acid secretion of the stigma which is the natural cause of 
its bursting. Moreover, to enable us to arrive at a general 
rule, it is necessary to employ a low magnifying power, so 
as to be enabled to examine a great number of pollen grains 
from a given plant at the same time ; because, if we examine 
them singly, we cannot hope to catch the type of their de- 
hiscence. 
I have not been able to cause the spores of any Acotyle- 
donous plant to dehisce in diluted acids. 
The grasses and sedges burst by a single organized pore 
in the exine; this was first observed by Fritzche. 
I am satisfied that the greater number of Monocotyledons 
burst by a long slit or chink in the eine, This is the case 
in the Aroidee, Typhacee, Smilacee, Colchicacee, Liliacee, 
Asphodelee, Amaryllidacee, Iridew, Commelinee and Butomee. 
In consequence of this method of dehiscence, the fovilla, 
after escaping, retains its form, either oval or spherical. 
The pollen of all Dicotyledons, perhaps with the excep- 
tion of the Conifere and Cycadee, burst by pores. I am 
aware that this statement is contrary to the opinion of 
Fritzche, who divides the pollens with double membranes, 
into those with and without organized openings in the 
exine. But he has himself figured appearances on the 
